Anyone here drives automatic car?
Discussion
Just wondering what is potential problem from driving an A/T car?
Driving A/T car is very nice and easy, especially driving around high traffic that so often put me in traffic jam where it needs to shift gear lower and higher. From RPM indicator I find that A/T have higher read than manual, say that it can reach 3000-4000 RPM easily while for the same case manual only runs at average 2000. I tend to avoid car runs at high RPM 4000 or higher, release the gas and pedal it again quickly to gain relative responsive power. Is this common?
Driving A/T car is very nice and easy, especially driving around high traffic that so often put me in traffic jam where it needs to shift gear lower and higher. From RPM indicator I find that A/T have higher read than manual, say that it can reach 3000-4000 RPM easily while for the same case manual only runs at average 2000. I tend to avoid car runs at high RPM 4000 or higher, release the gas and pedal it again quickly to gain relative responsive power. Is this common?
lenientism said:
Just wondering what is potential problem from driving an A/T car?
Driving A/T car is very nice and easy, especially driving around high traffic that so often put me in traffic jam where it needs to shift gear lower and higher. From RPM indicator I find that A/T have higher read than manual, say that it can reach 3000-4000 RPM easily while for the same case manual only runs at average 2000. I tend to avoid car runs at high RPM 4000 or higher, release the gas and pedal it again quickly to gain relative responsive power. Is this common?
Different systems will have different characteristics. Might help if you elaborated what type of vehicle you are referrring to.Driving A/T car is very nice and easy, especially driving around high traffic that so often put me in traffic jam where it needs to shift gear lower and higher. From RPM indicator I find that A/T have higher read than manual, say that it can reach 3000-4000 RPM easily while for the same case manual only runs at average 2000. I tend to avoid car runs at high RPM 4000 or higher, release the gas and pedal it again quickly to gain relative responsive power. Is this common?
stevieturbo said:
Different systems will have different characteristics. Might help if you elaborated what type of vehicle you are referrring to.
The head to head comparison was between auto Honda Fit 2002 and manual Toyota Cressida 1987, an old brick shaped car that I found it has more power and excitement from driving it. Another comparison of auto and manual might have similar characteristic. Steve_D said:
An auto will use higher revs to pull away as the torque converter is being used but once up to speed the revs should not be much different from a manual.
Steve
yes exactly, on the roads where enable the two cars running at optimum speed the RPM indicator are not too much different. The auto needs higher revs to pull away and there must be time lag from time pedaling the gas. The high revs on the auto will not be worrying me much now. Thanks. Steve
I owned 2 1.8e Engineed mk2 cavaliers. A CDi auto hatch weighing in at 1175KG and an SRi saloon weighing in at 1025Kg, and having what vauxhall refered to as an ultra close ratio gearbox.
The 3 speed auto was slow when cold, and had a gap as wide as latvia between 2nd and top. The Sri didn't and was great for overtaking. Both were woefully undergeared on the motyorway.
The 3 speed auto was slow when cold, and had a gap as wide as latvia between 2nd and top. The Sri didn't and was great for overtaking. Both were woefully undergeared on the motyorway.
If a search on teh Honda Fit is correct ( dont get the same name vehicle here )
It uses a CV transmission. No gears at all so to speak. So it will naturally tend to be revvy. ie, it revs to maximum torque, stays there as teh vehicle accelerates, which is controlled by the 2 pulleys within the CVT.
It is not like a conventional auto which does have different ratios.
A great system in theory, but dont think it was ever that fantastic in practice, and a little strange to drive too.
Only worse car I can think of, is a BMW auto, all they do is make the car rev its nuts off.
MY old Volvo 940 2.4td auto is great ( after I removed the kickdown linkage , revs a little, but not too badly, and doesnt shift unless its really provoked, making it very nice to drive.
It uses a CV transmission. No gears at all so to speak. So it will naturally tend to be revvy. ie, it revs to maximum torque, stays there as teh vehicle accelerates, which is controlled by the 2 pulleys within the CVT.
It is not like a conventional auto which does have different ratios.
A great system in theory, but dont think it was ever that fantastic in practice, and a little strange to drive too.
Only worse car I can think of, is a BMW auto, all they do is make the car rev its nuts off.
MY old Volvo 940 2.4td auto is great ( after I removed the kickdown linkage , revs a little, but not too badly, and doesnt shift unless its really provoked, making it very nice to drive.
Honda Fit was the first generation of Jazz, type people might be more familiar with. It has L and H lever actually, might work similar to the low and higher gear, although rarely used. Driving an auto shouldn't make us occupied as much as manual if we have to shift various gears.
Volvo 940/960 is still a temptation. If not an auto someone has offered me, perhaps I already had one before deciding a manual Cressida.
However removing kickdown feature I think it's rather a disadvantage, we might need it especially in awkward position for faster overtaking.
Volvo 940/960 is still a temptation. If not an auto someone has offered me, perhaps I already had one before deciding a manual Cressida.
However removing kickdown feature I think it's rather a disadvantage, we might need it especially in awkward position for faster overtaking.
blank said:
stevieturbo said:
It uses a CV transmission. No gears at all so to speak. So it will naturally tend to be revvy. ie, it revs to maximum torque, stays there as teh vehicle accelerates, which is controlled by the 2 pulleys within the CVT.
Have you ever driven a CVT?
If anyone has floored one in reverse they will agree.
I love my kickdown blank said:
stevieturbo said:
It uses a CV transmission. No gears at all so to speak. So it will naturally tend to be revvy. ie, it revs to maximum torque, stays there as teh vehicle accelerates, which is controlled by the 2 pulleys within the CVT.
Have you ever driven a CVT?
te. Is there a point to that question ?Edited by stevieturbo on Thursday 28th May 19:31
ANd its silly having a torquey turbodiesel engine, when all a kickdown does is make it try to rev. And most diesels dont like to rev.
I thought my old 525tds was the most ridiculous example of this. BMW claimed their super engine created its maximum torque at 1900rpm.
It was actually impossible to use any of this torque, as the auto box kept the engine around 25-4500rpm.
It was even a struggle to stay in top gear on the motorway. Anything below 70mph, and it was always in a lower gear, and ig you even hinted at pushing the go pedal, it kicked down a couple of gears, revving its nuts off again.
At least now with the kickdown removed ( In the volvo ) I can put my foot to the fllor to overtake, and makie use of the engines torque to do so.
Edited by stevieturbo on Thursday 28th May 19:35
stevieturbo said:
blank said:
stevieturbo said:
It uses a CV transmission. No gears at all so to speak. So it will naturally tend to be revvy. ie, it revs to maximum torque, stays there as teh vehicle accelerates, which is controlled by the 2 pulleys within the CVT.
Have you ever driven a CVT?te. Is there a point to that question ?Edited by blank on Friday 29th May 22:23
blank said:
stevieturbo said:
blank said:
stevieturbo said:
It uses a CV transmission. No gears at all so to speak. So it will naturally tend to be revvy. ie, it revs to maximum torque, stays there as teh vehicle accelerates, which is controlled by the 2 pulleys within the CVT.
Have you ever driven a CVT?te. Is there a point to that question ?Edited by blank on Friday 29th May 22:23
Really a CVT should keep the engine near maximum torque all the time it can... the lowest point of the bsfc curve is near the peak of the torque curve... the engine is operating at its most efficient there, hence generating max torque... gets more complicated when you throttle off for petrols but diesels more or less stay like that. A CVT should adjust its ratio to sit the engine at the lowest point of the bsfc curve for as long as you can get enough power out of it for your needs at the time, then lower its ratio to allow the engine to rev higher for more power when that much power is demanded.
One of my reasons for wanting to build a CVT-equipped vehicle is so that I can play with the engine/transmission control laws and how they are commanded by the throttle in order to get the best driving feel out of it, because I see no intrinsic reason why the feel should be crap.
One of my reasons for wanting to build a CVT-equipped vehicle is so that I can play with the engine/transmission control laws and how they are commanded by the throttle in order to get the best driving feel out of it, because I see no intrinsic reason why the feel should be crap.
stevieturbo said:
blank said:
stevieturbo said:
blank said:
stevieturbo said:
It uses a CV transmission. No gears at all so to speak. So it will naturally tend to be revvy. ie, it revs to maximum torque, stays there as teh vehicle accelerates, which is controlled by the 2 pulleys within the CVT.
Have you ever driven a CVT?te. Is there a point to that question ?Edited by blank on Friday 29th May 22:23
Perhaps I should have said "all the time during acceleration".
The ones I've driven haven't done.
Pigeon said:
Really a CVT should keep the engine near maximum torque all the time it can... the lowest point of the bsfc curve is near the peak of the torque curve... the engine is operating at its most efficient there, hence generating max torque... gets more complicated when you throttle off for petrols but diesels more or less stay like that. A CVT should adjust its ratio to sit the engine at the lowest point of the bsfc curve for as long as you can get enough power out of it for your needs at the time, then lower its ratio to allow the engine to rev higher for more power when that much power is demanded.
One of my reasons for wanting to build a CVT-equipped vehicle is so that I can play with the engine/transmission control laws and how they are commanded by the throttle in order to get the best driving feel out of it, because I see no intrinsic reason why the feel should be crap.
I've never seen a BSFC curve that looks like that. The ones I've seen always peak at low revs (generally lower than the full load peak torque speed) and high load. Whether that's a diesel with peak torque at 2000rpm, or a petrol with peak torque at 4500rpm.One of my reasons for wanting to build a CVT-equipped vehicle is so that I can play with the engine/transmission control laws and how they are commanded by the throttle in order to get the best driving feel out of it, because I see no intrinsic reason why the feel should be crap.
So the best point to keep it for driving at a constant speed would be a low engine speed (probably below peak torque) with a lot of load. As opposed to getting the same power with a higher engine speed and less load.
Have you got a BSFC curve that is lowest at the peak torque engine speed?
Edit:
This graph is for a VW 1.9 TDI:
Interestingly in that engine, best BSFC does coincide with peak torque (if you google some more pics you'll see a lot don't).
But...
If you're driving along at say 50mph, which needs say 20bhp, a CVT could put the engine at any speed/load combination on the 20bhp line. The peak torque engine speed would give a BSFC of about 230, but if you lowered the speed and upped the load you can get it down to somewhere between 200 and 210 at about 1200rpm.
Edited by blank on Saturday 30th May 12:31
Edited by blank on Saturday 30th May 12:33
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